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Adding Isolation Transformer

8/13/2005 11:44 AM
Adding Isolation Transformer
I have an old Silvertone "amp in case" model and wanted to add an iso tranny for safety purposes but haven't done so before. Any help would be greatly appreciated.  
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8/13/2005 7:50 PM
Mouser carries them for about $12  
Just wire the secondary to wherever the original power cord was tied down, and wire a new 3 wire cord with a ground to the primary (the green ground lead should be connected to the chassis). If you buy a Triad "World Series" model there are two primary windings so that it will operate on 120 or 240 VAC...for 120 VAC they are wired in parallel and the instructions will give the correct colors to attach together.
8/14/2005 10:11 PM

Thanks for the tips. I will start work on it next week.  
8/15/2005 11:46 AM
Jack Koochin

Does this mean it's run directly off the AC with no line isolation? If this is like an old Symphonics amp I added a xformer to, note that the top jack/face plate might not be directly tied to the chassis... it might be isolated with an R and a C. If this is the case, you need to GROUND the jack/face plate for safety, after adding the iso xformer, as this is where the guitar cord will get its ground.  
I'm no expert at this, but I did it successfully on the one Symphonics amp... Take a look at the schematic... you may be able to short out this R/C and have both the chassis and faceplate at ground (desirable for hum reasons). If you try shorting them out, you might try using a fast blow fuse as the short to test this out. I doubt there would be a difference in potential, but just to be sure...  
8/16/2005 11:53 AM

Very good point that I will double check.  
Thanks, TL
8/15/2005 11:00 PM

Look in Mouser, Allied, or your favorite electronisc parts supplier. Isolation transformers should be in the index. They will be in a separate section from other power transformers, so there should be no confusion.
8/16/2005 12:56 PM
Enzo and Ukiah
Would the Mouser 553-N51X from Ukiah's post be adequate? It's just a little dinker of an amp.  
Thanks, TL

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